1. Field of the Invention
The present invention relates generally to data buffering for recording and playback systems. More particularly, the invention relates to buffering systems and methods for use during optical writing and reading of data with respect to a storage medium, such as a flexible optical tape in an optical video recorder (OCR).
2. State of the Art
Presently, flexible tape for optical storage of data is known, as described in U.S. Pat. Nos. 4,719,615 and 4,912,696, both identified on their cover pages as being assigned to Optical Data, Inc. To optically record data on a medium such as a flexible optical tape, a beam of laser light is directed onto the tape. The laser beam melts the tape or burns holes in the tape to produce data spots representing bits of data. The data spots have a reflectance, transmittance or other optical characteristic which can be distinguished from the background of the optical tape.
Presently, optically sensitive tape has not been effectively used to record high frequency signals such as television video signals. One reason for this is the absence of an effective laser scanning system wherein data (e.g., analog video data) arriving at a constant input rate can be recorded uniformly (without gaps) on a medium (e.g., optical tape) moving at a constant speed.
Other known recording systems, such as facsimile systems, do not adequately address the problem at hand. While these systems may receive input data at a constant rate and record data on a moving paper medium, the medium is not continuously moving at a constant speed. Rather, the medium is moved incrementally so that a marking (i.e., printing) mechanism can print information as it is received.
Input data is received by a facsimile system during times when the marking (i.e., printing) mechanism is not positioned to print. Thus, the data is buffered (i.e., stored in memory) until the marking mechanism reaches the proper write location. The marking mechanism is able to print at a rate equal to or faster than the input data rate.
Typically, facsimile systems use at least three line-storage buffers. As input scan lines are received, they are stored at the input rate in each of the three buffers sequentially. Concurrently, the content of a previously loaded buffer is transferred to the printing mechanism at the faster printing rate. Thus, there is one buffer which is currently being filled from the input, a second buffer which is being emptied by the printer and a third buffer which is empty awaiting filling from the input.
Because emptying of the aforementioned second buffer is performed at a rate faster than the input (i.e., filling) data rate, there are times when the printing mechanism is ready for a new line but an output buffer has not been filled with new data. At these times, there are two empty buffers with the third still being filled from the input. When this occurs, the paper advancing mechanism is typically stopped to permit the line buffer system to catch up until a full buffer is available for printing.
Thus, although buffering techniques are generally well known for addressing timing problems in data recording systems, they have typically been designed for specific systems. Accordingly, the facsimile buffering system described above would not practically be applicable for use in an optical recording and playback system having a continuously moving recording medium. Unlike a facsimile system where the paper advancing mechanism can be stopped to permit the printing and buffering system to catch up, a uniformly moving optical tape can not be similarly operated.